Capacitor bank switching
Capacitor bank switching
(OP)
We have three power factor correction banks in the weak system (generator supply). We didn't have any issue when we were switching the first one on to the system. But we saw a transient overvoltage when we were switching the second one on. We haven't swicthed on the third one. I am afraid we may see a higher transient overvoltage in the system since the capacitors which are already in the system will back charge the third one being switched on. Does a stronger system help to mitigate this kind of overvoltage issue? Any inputs would be appreciated.





RE: Capacitor bank switching
If a stronger system implies a larger system, then yes.
Why are you worried about power factor on a generator? Not to imply that there are not valid reasons to consider power factor on a generator, but power factor is often less important on an islanded generator close to the load than on a grid.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Capacitor bank switching
RE: Capacitor bank switching
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Capacitor bank switching
What you have is the case switching a capacitor in parallel with one already charged. Without adequate current limiting reactors (or long cables), it will result in what you are seeing. When the second cap is switched on, it has it own charging current, plus the other caps also see it as a short circuit at time t=0+ and discharges through it. You need to install appropriate reactors in series with the caps. Talk to some cap manufacturers and they will help you.
Switching the first bank will not be an issue as you have already experienced.
Rafiq Bulsara
http://www.srengineersct.com
RE: Capacitor bank switching
Now I've left standing instruction with the DG operator not to switch on the cap bank when he is on DG power. No probs since then.
Muthu
www.edison.co.in
RE: Capacitor bank switching
Rafiq Bulsara
http://www.srengineersct.com
RE: Capacitor bank switching
We were not experiencing high inrush currents. we only saw high transient overvoltage upon switching the second.
RE: Capacitor bank switching
RE: Capacitor bank switching
If you are able to monitor the output of the AVR, you may see a voltage drop that somewhat reflects the voltage transient.
If you have an AVR on manual control (not possible with most AVRs that I work with) You would see a steady rise in voltage as the capacitors supply some of the exciting current to the generator. With the AVR in automatic mode, the AVR senses the voltage rise caused by the capacitors and reduces the AVR contribution to excitation accordingly. The transient over voltage that you are seeing is probably an indication of the AVR response to a step increase in terminal voltage, whether caused by load shedding or capacitor connection.
Bill
--------------------
"Why not the best?"
Jimmy Carter